The present invention relates to target tracking, and more particularly, to target angle measurement and tracking apparatus and methods which can isolate and maintain stable track on a selected target in a multiple-target environment.
The closest concept relating to single target tracking in a multiple-target environment comprises a combination of a target angular extent estimation coupled with off-boresight tracking. The target angular extent estimation may be used to detect the presence of multiple targets upon which off-boresight tracking may be commanded to deliberately place the desired target off the antenna boresight in order to put the undesired targets at the antenna null. However, the target angular extent estimation depends strongly on the relative signal strengths of the targets, i.e., multiple targets with a single dominantly strong target will appear as a single target. Off-boresight tracking, while reducing corruption from the undesired targets in measuring angle discriminant to the desired target, is more susceptible to thermal noise as the desired target is placed away from the boresight.
In multiple-target environments, signals received at the sum and difference channels are composites of individual targets. Therefore, using these composite signals results in an angle estimate about the targets' centroid. In addition, depending on their relative phases, these individual signals can add coherently or partially cancel each other, which yields large measurement variance. This results in inaccurate and unstable tracking.
Therefore it would be advantageous to have a target tracking method that independently provides for angle measurements to each individual target, and thus isolates and tracks a specified target in a stable manner.